The present invention relates to a solenoid valve (an electrically-controlled pneumatic valve), e.g. for controlling directional control valves in pneumatic systems.
In general, conventional types of solenoid valve comprise, in the most simple configuration, a body having a solenoid or electromagnet fixed therein with a plunger core carrying a valve member so as to move the valve member between a first position corresponding to an excited state of the electromagnet in which the valve member is spaced apart from its seat and puts two ducts into communication, and a second position corresponding to a non-excited state of the electromagnet in which the valve member is pressed against its seat and isolates the ducts from each other. Naturally, other types of solenoid valve also exist (e.g. having three ports and two positions) which, depending on the position of the valve member(s) serve to put one of two ducts selectively into communication with a third duct while isolating the other duct from the two in communication.
It is known to fit such a solenoid valve with a manual control pushbutton enabling the plunger core and the associated valve member to be brought into the first position in the absence of excitation of the electromagnet, e.g. for the purpose of performing adjustment operations.
A first type of pushbutton is mounted on the body transversely to the plunger core so as to slide between an active position in which a cam-forming end of the pushbutton co-operates with the plunger core and moves it into its first position, and an inactive position in which the pushbutton is returned resiliently and the cam-forming end is disengaged from the plunger core.
In a second type of pushbutton, of the bayonet kind, the pushbutton is mounted on the body firstly to slide between active and inactive positions like the pushbutton of the preceding type, and secondly, while it is in the active position, to pivot between a locked position in which the pushbutton co-operates with an abutment element secured to the body to prevent resilient return of the pushbutton into its inactive position, and an unlocked position in which the pushbutton escapes from the abutment element.
Pushbuttons of the first type are generally used in solenoid valves for associating with bistable directional control valves, whereas pushbuttons of the second type are generally used in solenoid valves for association with monostable directional control valves. Furthermore, the practices implemented by the users of solenoid valves have established preferences for one type or the other, and a manufacturer needs to comply with those preferences in order to satisfy the market as well as possible. The manufacturers of solenoid valves therefore need to have both types of pushbutton available, depending on the intended purpose of the solenoid valve, and even though the body structure of the valve is otherwise the same. This complicates the manufacture of such valves and gives rise to a relatively large amount of extra cost.
There thus exists a need that has not been resolved in satisfactory manner at present for a single manual control means for a solenoid valve which is simple to adapt as a function of the intended purpose of the valve on which it is mounted.
There also exists a need to change the manual access for adjustment and maintenance on a machine. While a machine is under development with qualified personnel, the possibility of locking manual controls in position is appreciated, whereas subsequently, in operation, it is preferred to eliminate any possibility of manual locking so as to ensure that unspecialized personnel cannot put the machine into a position where it can no longer operate properly.
To this end, the invention provides a solenoid valve comprising a body in which there is fixed an electromagnet having a plunger core carrying at least one valve member and movable between first and second positions corresponding respectively to an excited state and to a rest state of the electromagnet, and a manual control pushbutton mounted on the body transversely to the plunger core firstly to slide between an active position in which a cam-forming end of the pushbutton co-operates with the plunger core to bring it into its first position and an inactive position into which the pushbutton is returned resiliently and its cam-forming end is disengaged from the plunger core, and secondly while in the active position, to pivot between a locked position in which the pushbutton co-operates with an abutment element secured to the body which opposes resilient return, and an unlocked position in which the pushbutton escapes from the abutment element, the abutment element comprising means enabling it to be releasably fixed to the body.
When the abutment element is in place, the pushbutton can be locked in the active position like a bayonet pushbutton. The solenoid valve is then adapted to be used with monostable directional control valves or to satisfy users of a certain type. When the abutment element is withdrawn, the pushbutton cannot be locked in the active position and it operates like a simple pushbutton. The solenoid valve is then adapted to be used with bistable directional control valves or to satisfy other users. The solenoid valve is thus adapted to the type of directional control valve that it is to control in a manner that is particularly simple, either by leaving the abutment element for the manual control pushbutton in place or by withdrawing it. Furthermore, by means of this disposition, a solenoid valve is made available whose control can be lockable during an initial stage of use (machine being set up by specialized personnel) and which is no longer lockable for subsequent use (e.g. during normal operation of the machine) where the personnel is less specialized.
Advantageously, the abutment element is fixed to the body in a zone thereof which is accessible from the outside. The abutment element can then be withdrawn without any need to disassemble the valve, and it can be withdrawn quickly.
In a particular embodiment, the releasable fixing means comprise a breakable tab which is preferably arranged to break in twisting, the abutment element having an indentation suitable for co-operating with a screwdriver type tool. Withdrawal of the abutment element is then irreversible. Furthermore, the abutment element can be made integrally with the body, thus simplifying the structure of the valve and making it easier to manufacture.